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Date submitted2023-11-10
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Date accepted2024-05-02
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Date published2024-08-26
Paleoproterozoic Saltakh Pluton, Anabar Shield: mineralogical composition, age and a geodynamic setting
- Authors:
- Nikolai I. Gusev
- Lyudmila Yu. Romanova
The Saltakh Massif is located in the northern Anabar Shield, in the Saltakh shear-zone. It consists of two-pyroxene schists and plagiogneisses metamorphosed under granulite-facies conditions. Their chemical composition is consistent with that of a differentiated series of rocks ranging from gabbro to tonalites with abundant alaskitic gneissose granite veins and bodies. The rocks are mainly high-potassium (K2O/Na2O > 0.50), high-magnesium (mg# 50-70), low-titanium (TiO2 0.35-1.31 wt.%) with low TiO2 concentration in clino- and orthopyroxene. Normative olivine makes up 6-9 % of metagabbroic rocks. The rocks display well-defined negative Ti, Nb, Ta, and P anomalies typical of subduction magmatism. The two-pyroxene gneisses show high Sr/Y ratios of 67.6-88 and (La/Yb)N of 24.8-25.6. Saltakh rocks are part of a shoshonite series, as indicated by Nb/La, La/Yb, Th/Nb and Ce/Yb ratios. All the rocks display positive εNd(T) values of 1.9-4.1 and εSr(T) of 0.77-17.8 indicative of a mantle source of magma and T(Nd)DM of 2,20-2,26 Ga. U-Pb zircon dating (SHRIMP II) has shown that the protoliths of Saltakh melanocratic rocks were dated at 2100-2086 Ma, and those of two-pyroxene plagiogneisses of tonalite composition were dated at 2025±7 Ma. Alaskitic gneissose granites were dated at 1969±7 Ma. The study of the trace element composition of zircon has revealed general enrichment in LREE. High LREE concentrations are due to secondary zircon alterations and the shoshonitic pattern of the melt, the high-temperature conditions of crystallization, and an anomalous fluid regime. The geodynamic setting in which the Saltakh Massif was formed was consistent with a pericontinental magmatic arc. The formation of alaskitic gneissose granites was due to anatexis provoked by later collision processes. Saltakh magmatic rocks were formed simultaneously with magmatic rocks from the Khapchan prospect which occur farther south, and were studied earlier (2095±10 Ma tholeiitic metadiorites and 2030±17 Ma calc-alkaline metatonalites). We interpret them as part of a metamorphosed juvenile Paleoproterozoic suprasubduction complex.
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Date submitted2023-11-02
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Date accepted2024-03-05
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Date published2024-08-26
The polyphase Belokurikhinsky granite massif, Gorny Altai: isotope-geochemical study of zircon
Based on the isotopic-geochemical analyses of zircons from granites of the Belokurikhinsky massif in the Gorny Altai using the U-Pb method, the ages of three intrusion phases have been determined for the first time: the age of the first phase refers to the time interval of 255-250 Ma, the second and the third phases have similar ages of about 250 Ma. The formation time of the Belokurikhinsky massif is estimated as not exceeding 5-8 Ma. The δ18O values for zircons from granites of the second and the third intrusion phases average around 11.5-12.0 ‰, indicating a significant contribution of a crustal component in the formation of the parent melts for granites of these phases. The crystallization temperature values of the zircons by the Ti-in-zircon thermometer for three phases range from 820 to 800 °C. The P-T crystallization parameters of titanite from the first phase, determined using a titanite thermobarometer, average around 770 °C and 2.7 kbar. The zircons from the first phase mostly exhibits geochemical characteristics of typical magmatic zircons. The zircons from the second and the third intrusion phases either may be unaltered magmatic zircons or enriched in incompatible elements (LREE, Th, U, Ti, Ca, etc.) due to fluid influence, resembling hydrothermal-metasomatic type zircons in terms of their geochemical characteristics. A number of zircon grains from the second and the third phases of granites demonstrate anomalous geochemical characteristics – the REE distribution spectra atypical for zircons (including “bird's wing” type spectra with oppositely tilted of light and heavy REE distribution profiles), as well as significantly higher contents of certain trace elements compared to other varieties. Such an enriched zircon composition and wide variations in the incompatible element content are due to non-equilibrium conditions of zircon crystallization and evolution of the fluid-saturated melt composition during the final stages of the massif formation.
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Date submitted2022-04-11
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Date accepted2022-06-15
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Date published2022-07-26
Magma feeding paleochannel in the Monchegorsk ore region: geochemistry, isotope U-Pb and Sm-Nd analysis (Kola region, Russia)
A comprehensive study of a 340 m thick lenticular-sheet body of ultramafic composition penetrated by structural well M-1 at a depth of about 2.2 km was accomplished. Its main volume is composed of plagioharzburgite; fine-grained rocks of norite and orthopyroxenite chilling zones are preserved on endocontacts. The rocks of the body are similar in composition to the rocks near the underlying ore-bearing layered intrusion – the Monchepluton. The age of intrusion of the ultramafic body is 2510 ± 9 Ma (U-Pb, ID-TIMS, zircon) and, taking into account analytical errors, is comparable with the formation period of the Monchepluton (2507-2498 Ma). According to the study of the Sm-Nd system in rocks and minerals, a positive value of the e Nd (+1.1) parameter was established, similar to that in dunites and chromitites of the Monchepluton. Based on these results, the ultramafic body penetrated at depth was assigned to the magma feeding paleochannel through which the ultramafic, weakly contaminated magma entered the overlying magma chamber. This body is a unique example of a magma-feeding system for the ore-bearing layered intrusion of Precambrian age.
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Date submitted2022-04-04
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Date accepted2022-05-13
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Date published2022-07-13
Distribution of trace elements controlled by sector and growth zonings in zircon from a miaskite pegmatite of the Vishnegorsky massif, the Southern Urals
Data on the content and distribution of trace and rare-earth elements (SIMS method) in sectors and growth zones of a large zircon crystal from miaskite pegmatites of the Vishnegogorsky massif are presented. The morphology of the zircon crystal is a combination of a dipyramid {111} and prism {010}. It has been established that the growth sector of dipyramid {111} is characterized by almost one order of magnitude higher contents of Y, Nb, REE, Th; higher Th/U and Eu/Eu* values; REE distribution spectra are flatter compared to prism {010} growth sector. A regular decrease in the content of trace and rare-earth elements in the direction from the central zone to the marginal zone of crystal growth was revealed. A smooth regression of zircon crystallization temperature of zircon from 960 °C in the central zone to 740 °C in the marginal zone of the dipyramid sector and 700-650 °C in the prism sector has been revealed, which may be a reflection of thermal evolution of the crystallization process. It is assumed that crystallization of the central zone of zircon occurred at early stages from a relatively trace-еlement-rich melt. The crystallization was completed at lower temperatures, probably, simultaneously with the formation of REE-concentrating minerals, which resulted in natural decrease of content of trace and rare-earth elements in the melt and, consequently, in zircon crystallizing from it.
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Date submitted2020-07-27
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Date accepted2021-03-30
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Date published2021-06-24
New data on the granite pedestal of the monument to Peter the Great “The Bronze Horseman” in Saint Petersburg
In order to expand and popularize knowledge about the stone decoration of Saint Petersburg, we present new data on the mineralogy and petrography of the famous Thunder-Stone, the parts of which were the basis for the monument to Peter the Great – the legendary “Bronze Horseman”. In the course of studying geological documentation of the monument's granite base, we examined the mineral composition and internal structure of granite, as well as the fragments of a pegmatite vein and veinlets found in it. 25 single-mineral samples were collected from the available micro-scaled shear fractures within the pedestal surface and studied by electron microscopy, electron probe and X-ray phase analysis. It was established that K-Na feldspar in the granite composition was represented by microcline, whereas micas were represented by annite-siderophyllite and muscovite. Accessory minerals included monazite, xenotime, thorite, zircon, rutile, apatite, fluorite, Ti-, Nb-, Ta-bearing minerals, uranium phosphates. The presence of topaz is characteristic of pegmatites. The revealed structural and textural features of four granite boulders in the monument pedestal, as well as mineralogical and chemical composition of their rock-forming and accessory minerals, showed the similarity of this rock to Precambrian biotite-muscovite granites and topaz-containing pegmatites (stockscheiders) of the late formation phase of the Vyborg rapakivi granite massif. The research results are considered as the basis for further geological and mineralogical study of the Thunder-Stone origin and determining the place of its separation from the primary source.
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Date submitted2018-07-04
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Date accepted2018-09-17
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Date published2018-12-21
Secondary dispersion halos as a prospecting indicator of platinum metal mineralization on the example of the Kamenushinsky massif (Middle Urals)
- Authors:
- A. M. Minibaev
The paper discusses the results of bulk rock geochemical sampling of the Kamenushinsky massif eluvial-deluvial deposits and the massifs bedrocks spectral analysis data. Evaluation of secondary dispersion halos using two-dimensional modeling and multivariate statistic processing of the results have allowed establishing the spatial collocation of platinum and chromium anomalies and high correlation between these elements. These facts confirm the considerable contribution of chromite-platinum mineralization to the primary ores of the entire Kamenushinsky massif. The geological observations and rocks chemical composition analysis has revealed that uranium and barium anomalies are associated with the areas of gabbro and granitoids dike bodies. The insignificant overlapping of uranium and barium anomalies with platinum and chromium ones, as well as the negative correlation between these two groups of elements, is inconsistent with earlier conclusions on the spatial association of platinum mineralization with gabbro and granitoids dikes and a possible connection between these dikes and platinum metal mineralization zones.
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Date submitted2015-08-17
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Date accepted2015-10-18
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Date published2016-04-22
Platinum specialization of supergene nickel deposits on ultramafic massifs of the Urals
- Authors:
- I. V. Talovina
This paper presents an analysis of geochemical data obtained as a result of persistent research of the Buruktal, Ufalei, Elov and others supergene nickel deposits of the Urals on the content of precious metals. Content and distribution of platinum group elements, gold and silver in oxide–silicate nickel ores are compared with their content in initial dunite-harzburgite bedrock. It was revealed that all the PGE accumulate in supergene nickel deposits. Geochemical specialization of PGE mineralization of supergene nickel deposits is determined by palladium and platinum, while in dunite-harzburgite substrate of primary ophiolitic massifs major platinoids are ruthenium, osmium and iridium. Pt/Pd ratio is generally less than 1, i.e. palladium is dominating in them with some exceptions.
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Date submitted2010-07-17
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Date accepted2010-09-02
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Date published2011-03-21
Selection of parameters camouflet blasting to reduce bump hazard by development uranium deposits
- Authors:
- D. Yu. Dordzhiev
Simulation-based by the finite element values obtained stress strain state around the stope ore as ore body downstream horizontal layers with a mined-out space. The results of the simulation allowed to substantiate a contained blasting parameters to bring pillar to anti bump hazard state.
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Date submitted2009-09-15
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Date accepted2009-11-02
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Date published2010-06-25
Mathematical modeling of stress-strain state of the mined seam deposits
- Authors:
- A. P. Gospodarikov
- M. A. Zatsepin
Development of bedded deposits is associated with man-caused distortion of specific environment – the rock massifs, which are very complicated in their composition, can vary significantly in mechanical properties and is characterized with a wide variety of laws and techniques to assess its stress-strain state.
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Date submitted2009-09-19
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Date accepted2009-11-24
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Date published2010-06-25
The forecast of the stress-strain state of massifs rocks in the bed deposits
- Authors:
- A. P. Gospodarikov
- M. A. Zatsepin
The variety of the mining and geological conditions with further increasing in depth of the development of bedded deposits leads to necessity for the analysis of stress-strain state near different types of excavations.
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Date submitted2009-08-05
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Date accepted2009-10-06
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Date published2010-02-01
The problems of stratigraphy on devon оf Polar Urals and Pay-Hoi
- Authors:
- A. L. Zherlygin
The legends of the Polar Urals and Pay-Hoi map series were estimated for proving the mapped subdivisions due to geological survey in the scale 1:200000 conducted in Kara-Silovskaya area (on western slope of the Arctic Urals and the range Pay-Hoi). In the result it was found out that Eletskaya Structure-Formation Zone in Devon was divided into a great number of stratigraphic units, reflecting the lateral substance changes of the same age level. According to it all units are conventionally valid and there are same equal ones among them. The biohermal massifs are not distinguished as independent units.
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Date submitted2009-07-06
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Date accepted2009-09-18
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Date published2010-04-22
Simulation of the stress-strain state forming around the vertical mine in the field of tectonically fractured massif
- Authors:
- D. Yu. Dordzhiev
The influence of the front clean up of stress-strain state around a vertical mine of a tectonically fracture massif for a uranium deposit «Antey» is considered. By means of computer simulation it’s have been confirmed by field observations.